This invention relates to the field of machine vision, and its application in obtaining an optimally focused image of an object under analysis. Specifically, the invention addresses a need for obtaining an optimally focused image under high magnification of a portion of a transparent or translucent surface that is not perfectly flat, though, it can be used to inspect the surface of virtually any object.
Inspection operations in an industrial environment are typically performed to characterize manufacturing operations, and to ensure that quality and product specification requirements are met. Many inspection operations can be extremely tedious for human operators performing manual inspection, and the application of machine vision is typically used to improve the consistency and accuracy of an inspection operation, while relieving an inspection operator from performing the task. For example, the application of machine vision-assisted inspection of fiber optic cable assemblies has recently been the subject of much development.
Fiber optic cable assembly operations require the inspection of fiber optic cable end faces to ensure that fiber connections do not degrade optical signal transmission. Scratches, cracks, and debris on critical areas of the interconnection interface may result in defective operation, or result in a degradation of performance. High-magnification inspection of the fiber end face is typically performed during assembly to inspect the condition and cleanliness of the fiber.
Inspection of the end face of a fiber optic cable is inherently difficult because of the properties and characteristics of the fiber. The regions of the fiber end face that require inspection are generally translucent, and exhibit low contrast of features when imaged for machine vision applications. The translucent nature of the fiber optic cable contributes to difficult lighting conditions since illumination intended for inspection of the surface also enters the fiber, and may reflect back into the machine vision system, causing image noise. Moreover, images of similar fiber ends typically appear significantly different under identical lighting conditions.
Automation of the inspection of fiber optic cable end faces using machine vision improves efficiency, and minimizes and/or avoids the subjectivity of human assessment. Effective implementation of machine vision in an automated inspection process requires a properly focused image of the area under analysis. However, since the fiber end surface is typically non-planar, it is difficult to acquire a single image of the fiber end surface for inspection that is optimally focused, because the depth of field at high magnification is typically less than the extent to which the surface is non-planar.
To provide an optimally focused image of planar fiber end surfaces, the prior art suggests the combination of images acquired at different focus planes in front of and behind an optimal focus position. While this method is effective for evaluation of surface features having a non-zero depth, its utility is limited to planar surfaces. Other known methods suggest the acquisition of multiple sectional images from a single focus setting, and combining the sectional images into a single combined image, though such an apparatus can be extremely complex.
Thus, a need exists for the capability of generating an image in an optical inspection system of a non-planar surface from a single image acquisition source.